How do you figure out what the atomic radius is of an element? The atomic radius for Li is 123 pm?

In my book it shows the atomic radius for some of the elements, here are some of the examples, Na 157 pm, K 203 pm, Rb 216 pm, Cs 235 pm, How do they come up with these number for the atomic radius, any help would be appreciated. ThanksHow do you figure out what the atomic radius is of an element? The atomic radius for Li is 123 pm?
first hyperlink is a list of all elements in order or atomic radius


second hyperlink is the explanation you were looking for.


I know this helped!How do you figure out what the atomic radius is of an element? The atomic radius for Li is 123 pm?
They measure the distance between two nuclei, so if you took a chunk of Lithium and measured the distance between two lithium nuclei using X-ray diffraction and divided it by two you'd have the radius.